A vivid animation based on data from ESA’s ERS-2 satellite
shows the onset of the recent El Nino phenomena from July
to December of last year.

Covering a large area of the Pacific Ocean from South
America to Australia and southeast Asia, the animation
demonstrates the three most important factors that mark
a phenomenon that can shape weather patterns from South
America to Australia, and from India to southeast Asia:

  • * sea surface temperature
  • * sea surface levels
  • * winds

Surface water temperature is represented as deviations
from average temperature values by the colour of the water
surface. The greenish-blue colour represents the average
temperature of the water. The purple colour represents a
temperature 8 deg. Celsius above average, while the blue
represents the other extreme of the scale, 8 deg. Celsius
below average.

The height of the ocean water, as a deviation from average
levels, is seen by the shape of the sea surface, an effect
that is difficult to see because of the compression of the
video. The ‘wave’ effect of the surface represents the
amplified deviation of the water’s surface from its
average height; the highest ‘waves’ display deviations
from the average of about 1.8 metres.

The wind is shown as blue arrows. Trade winds in the area,
blowing constantly from east to west, are clearly visible,
particularly in the final months of 2002. Winds blowing
in this direction, pushing warm surface water to the
west, is consistent with a weak, or weakening, El Nino.

El Nino expected to weaken

According to the US National Weather Service’s Climate
Prediction Center (CPC), El Nino conditions continued
during January 2003, but there were indications that the
warm episode is beginning to weaken.

"Consistent with current conditions and recent observed
trends, most coupled model and statistical model forecasts
indicate that El Nino conditions will continue to weaken
through April 2003," the CPC forecast states. "Thereafter,
the consensus forecast is for near-normal conditions
during May-October 2003."

The animation incorporated data from several ERS-2
instruments. Sea level measurements were obtained by the
radar altimeter, an active microwave sensor designed to
measure return echoes from ocean and ice surfaces.
ERS-2’s Along Track Scanning Radar (ATSR) acquired the
data on temperatures of the sea surface temperatures.
The European Centre for Medium-Range Weather Forecasts,
an international organisation for weather data, provided
the wind data used in the animation.

What causes El Nino?

In Spanish El Nino means ‘the Christ Child’ — a name
given to it by the Peruvian fishermen who hundreds of
years ago noticed how sometimes their coastal waters
grew unusually warm and fish grew scarce around
Christmas time. They had no way of knowing they were
naming a vast weather pattern whose effects strike much
of the globe.

El Nino is an irregular oscillation in tropical Pacific
currents, around the Equator. Usually, the wind blows
in a westerly direction in this region. This pushes the
warmer surface water into the western Pacific (which
can be as much as a half-meter higher than surface
levels in the east). In the eastern Pacific, colder
water from below the ocean’s surface is pulled up from
below to replace the water pushed west. So, the normal
situation is warm water (about 30 C) in the west, cold
(about 22 C) in the east.

In an El Nino, the winds pushing that water to the west
get weaker. With thermal circulation some of the warm
water piled up in the west is released and moves back
east, and not as much cold water gets pulled up from
below. This makes the water in the eastern Pacific
warmer, an El Nino trademark.

El Nino doesn’t stop there. Warmer ocean waters weaken
the winds, which in turn further warms the water, a
cycle that makes El Nino even stronger. This can have
wide-ranging consequences on climate patterns around
the world. These can include vastly increased rainfall
in South America, drought in Australia and fires across
southeast Asia, dying coral reefs in India, severe
winter storms in California, a heat wave in Canada and
intense hurricanes raging along the Pacific Ocean.

This phenomenon seems to occur every three to seven years.
The El Nino of 1997-98 is estimated to have caused more
than Euro 30,000 million of global property damage and
an unknown toll in human lives.

Several versions available

Several high-resolution versions of the animation are
available in Windows (.avi) and Quicktime (.mov) formats
(please be patient while they load). To view the animation,
click on the preferred version.

* 160×120 resolution:

Windows (2.8MB)
http://ravel.esrin.esa.it/video/nino7.avi

QuickTime (3.6MB)
http://ravel.esrin.esa.it/video/nino7.mov

* 320×240 resolution:

Windows (9.6MB)
http://ravel.esrin.esa.it/video/nino6.avi

QuickTime (9.5MB)
http://ravel.esrin.esa.it/video/nino6.mov

Related articles

* Satellite eyes focus on El Nino
http://www.esa.int/export/esaCP/GGGN8H2UGEC_FeatureWeek_0.html
* El Nino is yawning
http://www.esa.int/export/esaSA/ESANWPVTYWC_earth_0.html

Related links

* Protecting the environment
http://www.esa.int/export/esaCP/Protecting.html
* El Nino
http://earth.esa.int/eeo4.20104

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/export/esaSA/SEMY0J2A6BD_earth_1.html]
Several high-resolution versions of the animation are
available in Windows (.avi) and Quicktime (.mov) formats
(please be patient while they load). To view the animation,
click on the preferred version. Credits: ESA

[Image 2:
http://www.esa.int/export/esaSA/SEMY0J2A6BD_earth_1.html#subhead1]
Villages from Lake Murray Station in the Western Province
of Papua New Guinea carry rice sacks which were delivered
by an Australian Chinook helicopter, Sunday, Nov. 2,
1997. More than 100 Australian army and air force
personnel were involved in the distribution of emergency
food supplies to an estimated 56,000 people due to a
severe drought that is gripping the country. The unusual
weather patterns have been attributed to the El Nino
effect. Credits: AP Photo-David Gray, Pool

[Image 3:
http://www.esa.int/export/esaSA/SEMY0J2A6BD_earth_1.html#subhead3]
A river bed is cleaned as part of a program to combat
the effects of El Nino-caused weather in Tumbes in
northern Peru on Sunday, November 23, 1997. Credits:
AP Photo-Patricia Altamirano